Light Output and Single Photoelectron Studies of LYSO Crystals for the Barrel Timing Layer at the Compact Muon Solenoid

The Large Hadron Collider (LHC) is undergoing major renovations to increase its integrated luminosity. This will have a proportional increase the frequency of particle collisions at the Compact Muon Solenoid (CMS) experiment. As a result, CMS is planning to install a Barrel Timing Layer (BTL) composed of LYSO scintillation crystals to achieve a 30 ps timing resolution. The goal is to distinguish particle tracks from different primary proton-proton interactions that occur near each other spatially. The timing resolution highly depends on the scintillation light output. We construct a modular testing device that takes light output measurements from 16 different LYSO crystals at a time. The light output is measured by taking the ratio of a 0.511MeV signal from sodium-22, and the signal from single photoelectrons (SPEs). In the BTL production stage, the SPE signal will need to be measured with randomly occurring (dark) SPEs. However, there exist alternative methods using controlled sources of light that can be used to induce SPE generation, yielding a more accurate signal measurement. I have written software that aims to robustly take SPE and light output measurements using both the dark and light-induced methods, and found the error in the dark method to be 2.78%±0.93% with 95% confidence. The software will be used by several institutions around the world to measure the light output of thousands of LYSO detector modules.